1. Field of the Invention
This invention pertains to the field of coatings for high-temperature structural materials. This invention comprises the technology, where mainly physical vapor deposition, sputtering in a vacuum and thermal spray processes, are used for production of hollow protective thermal-barrier coatings functioning as high-temperature heat-exchangers, which coatings can be used, e.g., for thermal barrier protection of gas turbine engine blades and other components against degradation by high-temperature oxidation and hot corrosion.
2. Background
Generally, the following described process is used to fabricate a surface heat-exchanger on the substrate of a component: open channels for heat-carrier are made on the surface of the component's material (substrate), then these channels are filled by an extractable filler to the surface level, and the whole of the obtained surface is covered by an unbroken/continuous layer of a material, making an outer shell (the cover), covering the channels, after which the filler is extracted from the channels, and a surface heat-exchanger, as described below, is obtained, consisting of an outer shell, covering open channels cut into the substrate body. The shaping of the open channels in the substrate body is produced by various techniques, e.g., during the casting of the component, or formed by mechanical or electromechanical machining. The channels are filled by an extractable filler, usually, in a paste form. The filler prevents the deposited material of the outer shell from getting into the channels. The formation of the outer shell may be accomplished using various techniques of coating application, e.g., thermal spray, or physical vapor deposition. The material, of which the outer shell is formed, is chosen based on the specific functions to be carried out by the protected component, (e.g., UK Patent Application GB 2172060 A, INT CL F01D 5/00, by Rolls Royce Ltd.; Germany, Patent Application DE 37 06 260, INT CL F 01 D 5/18, by Siemens AG; Japan, Patent Application 61-25 881, INT CL F 01 D 5/18).
In the prior art, surface heat-exchangers are used in various fields when a decrease or an increase of surface temperature of a component is required; chiefly of specific components operating in severe temperature and/or mechanical stress conditions. Also known and used is the method of mounting ready-made heat-exchangers onto the surface of a component.
Usually the elements of such heat-exchangers are produced by the stamping technique and are fixed onto a component surface by soldering or welding. But such heat-exchange surfaces are complex to manufacture and unreliable in operation, which is why they are limited for practical use and cannot be used for gas-turbine engine (GTE) blades, and similar components operating in severe temperature and mechanical stress conditions. Development of effective, reliable surface heat-exchangers possessing a range of protective coating properties is a continual challenge in airspace, power-generation, and rocket technologies.
To adequately describe and illustrate the problem being considered, observation of the use of such surface heat-exchangers for protection of GTE blades from overheating will suffice.
In modern GTE and GTU (gas-turbine units), operational temperatures are more than 1000.degree. C. Improving economic operation and efficiency of a gas-turbine requires an increase in operating temperatures, which could be provided either by cooling GT components during operation, or by using materials with higher temperature and stress resistant properties.